TFD LCD device with high aperture ratio

ABSTRACT

Metal-Insulator-Metal (MIM) diodes in back-to-back thin film diode (TFD) liquid crystal display (LCD) device are formed on dual selective lines respectively. A transparent conductive layer on a first substrate comprises a pixel electrode, a first bottom layer, a second bottom layer, a third bottom layer, and a fourth bottom layer. A semiconductor insulator layer with a first contact hole on the first bottom layer and a second contact hole on the third bottom layer covers the first substrate and the transparent conductive layer. A metal conductive layer comprises a first selective line, a second selective line, a first top layer, and a second top layer, wherein an overlapped region between the first bottom layer and the first top layer is a first MIM diode, an overlapped region between the second bottom layer and the first top layer is a second MIM diode, an overlapped region between the third bottom layer and the second top layer is a third MIM diode, and an overlapped region between the fourth bottom layer and the second top layer is a fourth MIM diode. The first selective line electrically connects to the first bottom layer via the first contact hole, and the second selective line electrically connects to the third bottom layer via the first contact hole. The first and second top layers respectively isolated to the first and second selective lines are in the conformation of the first and second selective lines respectively.

FIELD OF THE INVENTION

The present invention relates to thin film diode (TFD) liquid crystaldisplay (LCD) device, and more particularly to a high aperture TFD LCDdevice.

BACKGROUND OF THE INVENTION Description of the Prior Art

Nowadays liquid crystal display (LCD) devices are widely applied indaily life, such as display devices of PAD, PC, Notebook, TV, electronicwatches, digital clocks, operating interface of copy machines, orodometer and speedometer in car interior with LCD thereon. LCD deviceshave monochrome display and passive driving circuits from earlier periodto now with more than 64K levels and active driving circuits to promoteapplications of LCD devices.

Present LCD devices are using active driving circuits to drive liquidcrystal. Thin film transistors (TFT) are commonly used to controlalignment of liquid crystal in active LCD devices. Nevertheless,fabrication of TFT is complicated due to 4 to 5 photolithographicprocesses are required. Further, very complicated half-tone lithographicprocess or other trick lithographic process is introduced to reducenumeral lithographic processes, but LCD panel manufacture yield islowered down.

One method for manufacturing active driving circuits is using thin filmdiode (TFD) as driving entity. Several advantages, such as simplestructure as well as process, and higher yield, are shown within TFD, asshown in U.S. Pat. Nos. 5,926,236 and 6,008,872.

However, the current-voltage diagram is asymmetric in the above TFD,which encounters some issues in driving circuits. Moreover, remnantshade and inhomogeneous gray scale also happens here. Four TFDs are usedto improve above issues, as shown in FIG. 1. A pixel cell 10 comprises aliquid crystal capacitor 20, 4 metal-insulation-metal (MIM) diodes 25,26, 27, and 28, two selecting lines (also known as scanning lines) 12,14, and a data line 60, wherein the liquid crystal capacitor 20comprises a pair of pixel electrodes 21, 22, and liquid crystal molecule23 between the pair of pixel electrodes 21, 22. This kind of structureis know as dual-select back-to-back TFD device, in which current-voltagediagram will be symmetric, as shown in FIG. 2. Related technique can bereferred to U.S. Pat. Nos. 6,225,968, 6,243,062, JP publication2002-043657, 2000-098429, 11-305267, TW publication 571169, 500947, andEPO 434627.

However, there is still issue here to be improved in dual-selectback-to-back TFD device. As shown in FIG. 3, a portion of liquid crystalcell 10 in FIG. 2 is shown in schematic representations. A pixelelectrode 21, four MIM diodes 25, 26, 27, and 28, and two selectinglines 12, 14, which all are on an active substrate, are shown in FIG. 3.Another pixel electrode 22, and data line 60 in FIG. 1 are on colorfilter substrate. When the active substrate and the color filtersubstrate are sealed, liquid crystal molecule will be injected into aspace between the two substrates to form an LCD panel. Four TFDs 25, 26,27, and 28 occupy a portion of pixel electrode 21, so that the pixelaperture is reduced.

Hence, a novel structure is necessary to increase pixel aperture for theMIM diode structure and also maintains simple process as well as highmanufacture yield.

SUMMARY OF THE INVENTION

For the invention background mentioned above, the conventional TFDdevice that create many problems and drawbacks. The main purpose of thisinvention is to provide a high aperture TFD LCD device. The fourback-to-back diodes are designed on selecting lines to increaseaperture. Manufacture method is to form a transparent conductive layeron a glass substrate as a pixel electrode and a first metal layer of theTFD first. A semiconductor insulation layer is then formed thereon. Ametal layer is formed on the semiconductor insulation layer as selectinglines, and back-to-back diodes formed within the selecting lines.

It is another object of this invention that simple process and highyield can be kept.

According to the objects above, this invention provides a thin filmdiode LCD device with high aperture ratio, which comprises a firstsubstrate, a second substrate and liquid crystal molecule between thefirst substrate and the second substrate. The first substrate comprisesa transparent conductive layer thereon, a semiconductor insulation layeron the transparent conductive layer and the first substrate, and a metallayer on the semiconductor insulation layer the transparent conductivelayer comprises a first pixel electrode, a first bottom layer, a secondbottom layer electrically connected to the first pixel electrode, athird bottom layer, and a fourth bottom layer electrically connected tothe first pixel electrode. The semiconductor insulation layer, coveringthe first substrate and the transparent conductive layer, has a firstcontact opening on the first bottom layer and a second contact openingon the third bottom layer. The metal layer has a first scanning line, asecond scanning line, a first top layer, and a second top layer, whereinthe first scanning line electrically connects to the first bottom layervia said first contact opening and has a first indentation, and thesecond scanning line electrically connects to the third bottom layer viathe second contact opening and has a second indentation. The first toplayer electrically isolating to the first scanning line is within thefirst indentation, and the second top layer electrically isolating tothe second scanning line is within the second indentation. Overlappedregion of the first bottom layer and the first top layer is a first MIMdiode, overlapped region of the second bottom layer and the first toplayer is a second MIM diode, overlapped region of the third bottom layerand the second top layer is a third MIM diode, and overlapped region ofthe fourth bottom layer and the second top layer is a fourth MIM diode.

The second substrate comprises a second pixel electrode thereon, and adata line electrically connecting to the second pixel electrode andabout perpendicular to the first and second scanning line. The secondpixel electrode overlaps to the first pixel electrode when the firstsubstrate and the second substrate are sealed.

In this invention, an active device for controlling a LCD devicecomprises a first scanning line, a second scanning line, a first MIMdiode, a second MIM diode, a third MIM diode, a fourth MIM diode, and apixel electrode. The pixel electrode is electrically connected to oneend of the second MIM diode and one end of the fourth MIM diode. Thefirst scanning line is electrically connected to one end of the firstMIM diode and has a first indentation; the second scanning line iselectrically connected to one end of the third MIM diode and has asecond indentation. The other end of the first MIM diode is electricallyconnected to the other end of the second MIM diode; the other end ofthird MIM diode is electrically connected to the other end of the fourthMIM diode. The first MIM diode and the second MIM diode are within thefirst indentation of the first scanning line; the third MIM diode andthe fourth MIM diode are within the second indentation of the secondscanning line.

This invention provides a method for manufacturing an active device forcontrolling a liquid crystal display device, which comprises a step ofdepositing a transparent conductive layer on a first substrate. Then,the transparent conductive layer is defined as a pixel electrode region,a first bottom layer, a second bottom layer electrically connected tosaid pixel electrode region, a third bottom layer, and a fourth bottomlayer electrically connected to said pixel electrode region. Next, asemiconductor insulation layer is deposited on said first substrate andsaid transparent conductive layer. A first contact opening is formed onsaid first bottom layer, and a second contact opening is formed on saidthird bottom layer. A metal layer is then deposited on saidsemiconductor insulation layer. The metal layer is defined as a firstscanning line, a second scanning line, a first top layer, and a secondtop layer, wherein said first scanning line electrically connects tosaid first bottom layer via said first contact opening and has a firstindentation, and said second scanning line electrically connects to saidthird bottom layer via said second contact opening and has a secondindentation, wherein said first top layer is within the firstindentation of the first scanning line and isolated therewith, and saidsecond top layer is within the second indentation of the second scanningline and isolated therewith, wherein overlapped region between saidfirst bottom layer and said first top layer is a first MIM diode,overlapped region between said second bottom layer and said first toplayer is a second MIM diode, overlapped region between said third bottomlayer and said second top layer is a third MIM diode, and overlappedregion between said fourth bottom layer and said second top layer is afourth MIM diode.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a schematic representation of a pixel cell electriccircuits of a conventional back-to-back TFD LCD;

FIG. 2 illustrates a schematic representation of current-voltage diagramof a conventional back-to-back TFD LCD;

FIG. 3 illustrates a schematic representation of active devices,scanning lines, and pixel electrode on a first substrate of aconventional back-to-back TFD LCD;

FIG. 4 shows flow chart of this invention in each stage;

FIGS. 5A to 5C illustrate a schematic representation of top views ofeach process stage in accordance with this invention; and FIG. 5Dillustrates a schematic representation of a pixel cell electric circuitsof a present back-to-back TFD LCD; and

FIGS. 6A to 6E illustrate a schematic representation of sectional viewsof each process stage in accordance with this invention

DESCRIPTION OF THE PREFERRED EMBODIMENT

Some sample embodiments of the present invention will now be describedin greater detail. Nevertheless, it should be recognized that thepresent invention can be practiced in a wide range of other embodimentsbesides those explicitly described, and the scope of the presentinvention is expressly not limited except as specified in theaccompanying claims.

Moreover, the dimensions of drawings only for reference due to they havebeen exaggerated and simplified.

TFDs are formed within scanning lines in this invention to increase LCDaperture without occupying area of pixel electrode.

A novel dual select back-to-back TFD structure for LCD device and methodthereof are provided. The manufacture process, as shown in FIG. 4,comprises a step of depositing a transparent conductive layer on a firstsubstrate, in which the transparent conductive layer can be ITO (indiumtin oxide) or IZO (indium zinc oxide). The transparent conductive layeris then defined to form a pixel electrode, and four bottom layers offour MIM diodes. The define process includes photolithographic andetching steps to transfer patterns to the transparent conductive layerto form the pixel electrode and the four bottom layers. Two bottomlayers of the four bottom layers of the four MIM diodes electricallyconnect to the pixel electrode respectively. Another two bottom layersof the four bottom layers of the four MIM diodes physically isolate tothe pixel electrode respectively. A semiconductor insulation layer isthen deposited to cover the pixel electrode, four bottom layers of thefour MIM diodes, and the first substrate, in which the semiconductorinsulation layer can be silicon nitride, or other material that provideselectric isolation and as insulation layer in the MIM diodes. Thesemiconductor insulation layer is defined to form two contact openingson two of the four bottom layers of the four MIM diodes, in whichneither the two bottom layers electrically connect to the pixelelectrode. Next, a conductive layer, which is metal, is deposited on thesemiconductor insulation layer. The conductive layer is then defined toform two selecting lines on two bottom layers of the four MIM diodes,and two top layers of the four MIM diodes, wherein the two top layers ofthe four MIM diodes are electrically isolated to the two selecting linesand disposed on the first substrate and within the indentations of thetwo selecting lines. Similarly, this step also includes lithographicprocess and etching step to form necessary patterns.

The following illustrates one embodiment of this invention shown in FIG.4, that FIG. 5 shows top view of schematic representation of each stepand FIG. 6 shows cross-sectional view of schematic representation ofeach step in accordance with dash line AB in FIG. 5.

FIG. 5A shows a pixel electrode 122, a first bottom layer 130-1, asecond bottom layer 132-1, a third bottom layer 134-1, and a fourthbottom layer 136-1 of four MIM diodes. FIG. 6A shows cross-sectionalview in accordance with dotted line AB in FIG. 5A. A transparentconductive layer is deposited on an active substrate 102, and defined toa pixel electrode 122 and a first bottom layer 130-1, a second bottomlayer 132-1, a third bottom layer 134-1, and a fourth bottom layer 136-1of four MIM diodes by using photolithographic process and etching step,in which the second bottom layer 132-1 and the fourth bottom layer 136-1are electrically connected to the pixel electrode 122, and the firstbottom layer 130-1 and the third bottom layer 134-1 are physicallyisolated to the pixel electrode 122. General photolithographic processcomprises photoresist coating, soft bake, exposure with mask, develop,hard bake, and photoresist strip. Developed photoresist has the samepattern to the mask, and an etching step is performed to transferpatterns of pixel electrode and the four bottom layers to thetransparent conductive layer. The etching step can be wet etching or dryetching, in which the transparent conductive layer has the same patternsto the photoresist layer. Then, the photoresist layer is removed.

In FIG. 6A, portion A shows schematic representation of sectional viewalong with the first bottom layer 130-1, and portion B show sectionalview along with the second bottom layer 132-1 and portion of pixelelectrode 122. The first bottom layer 130-1 and the second bottom layer132-1 are electrically isolated between the two dotted lines.

When using backlight, the active substrate 102 can be glass, ortransparent polymer. The so called active substrate is due to activedevices, which are diodes in this invention, are formed on thesubstrate. Another substrate is called color filter substrate generallydue to color filter, in FIG. 5D, a schematic representation of a pixelcell electric circuits of a present back-to-back TFD LCD, the otherpixel electrode 222 and data lines 60′ are formed on the other substrateand are electrically connected to the other substrate. The color filtersubstrate is also called passive substrate, because all devices thereonare passive device. The transparent conductive layer can be, forexample, ITO or IZO, formed by using vacuum evaporation or sputtering.For example in sputtering, indium oxide and tin oxide are formedpreviously, and then both powder of indium oxide and tin oxide aresintered to indium tin oxide target. Glow discharge is generated byargon in a vacuum chamber to make Ar+ ions impact to cathode indium tinoxide target, such that indium tin oxide will be sputtered to anodicglass substrate to form ITO film.

Then, as shown in FIG. 6B, a semiconductor insulation layer 104 isdeposited to cover the active substrate 102, the pixel electrode 122,the first bottom layer 130-1, the second bottom layer 132-1, the thirdbottom layer 134-1 (not shown in FIG. 6B), and the fourth bottom layer136-1 (not shown in FIG. 6B) of the four MIM diodes. This step will beeasier to be interpreted by using sectional view than top view, so onlysectional view is illustrated. Semiconductor insulation layer 104provides a middle insulation layer of the four MIM diodes. Thesemiconductor insulation layer 104 can be silicon oxide, siliconnitride, silicon oxynitride, tantalum oxide, silicon carbide alloy, orother material, or a combination of the above materials. Silicon nitrideis commonly used for better current-voltage characteristic. Plasmaenhanced chemical vapor deposition (PECVD) method is usually utilized toform silicon nitride.

Then, the semiconductor insulation layer 104 is defined to form a firstcontact opening 131 on the first bottom layer 130-1, and a secondcontact opening 135 on the third bottom layer 134-1, as shown in FIG. 5Band FIG. 6C. Portion of the semiconductor insulation layer 104 on thepixel electrode 122 is also removed. In this stage, similarphotolithographic process and etching step are used, and only maskpatterns are changed to contact the opening patterns and the pixelelectrode pattern. Further, appropriate etchant are used to remove aportion of semiconductor insulation layer 104.

Next, a conductive layer 106 is formed on the semiconductor insulationlayer 104, as shown in FIG. 6D. This step will be easier to beinterpreted by using sectional view than top view, so only sectionalview is illustrated. Only metal can be used as conductive layer 106,which can be aluminum, chromium, molybdenum, or other conductive metal,or alloy of the above materials. Formation of the conductive layer 106can be sputtering or vacuum evaporation.

Then, the conductive layer 106 is defined as a first scanning line 140,a second scanning line 142, and a first top layer 141, a second toplayer 143 of the four MIM diodes, as shown in FIG. 5C and FIG. 6E. Thefirst scanning line 140 electrically connects to the first bottom layer130-1 via the first contact opening 131 and has a first indentation140-1 at an edge of the first scanning line 140, and the firstindentation 140-1 faces a side of the first pixel electrode 122 andexpands towards an opposite edge of the first scanning line 140. Thefirst bottom layer 130-1 is disposed on the first substrate 102 andelectrically connected to the first scanning line 140. The secondscanning line 142 electrically connects to the third bottom layer 134-1via the second contact opening 135 and has a second indentation 142-1 atan edge of the second scanning line 142, and the second indentation142-1 faces another side of the first pixel electrode 122, and expandstowards an opposite edge of the second scanning line 142. The thirdbottom layer 134-1 is disposed on the first substrate 102 andelectrically connected to the second scanning line 142. In this stage,similar photolithographic process and etching step are used, and onlymask patterns are changed to scanning line patterns and top layerpatterns. Further, appropriate etchant are used to remove a portion ofconductive layer 106. The first top layer 141 is physically andelectrically isolated to the first scanning line 140 and the second toplayer 143 is physically and electrically isolated to the second scanningline 142 in this invention. Moreover, the first top layer 141 and thesecond top layer 143 are disposed on the first substrate and within thefirst indentation 140-1 of the first scanning line 140 and the secondindentation 142-1 of the second scanning line 142 respectively, suchthat a first TFD 130, which is sequentially composed of the first bottomlayer 130-1, the semiconductor insulation layer 104 and the first toplayer 141, and a second TFD 132, which is sequentially composed of thesecond bottom layer 132-1, the semiconductor insulation layer 104 andthe first top layer 141, are disposed on the first substrate and withinthe first indentation 140-1 of the first scanning line 140, and a thirdTFD 134, which is sequentially composed of the third bottom layer 134-1,the semiconductor insulation layer 104 and the second top layer 143, anda fourth TFD 136, which is sequentially composed of the fourth bottomlayer 136-1, the semiconductor insulation layer 104 and the second toplayer 143 are disposed on the first substrate and within the secondindentation 142-1 of the second scanning line 142. Equivalent circuitsof the TFD structure in this invention will be equivalent to FIG. 1, butpixel electrode 122 will have greater area than prior arts shown in FIG.3. When the active substrate 102 and the color filter substrate aresealed and has a plurality of liquid crystal molecules between theactive substrate 102 and the color filter substrate, the other pixelelectrode 222 overlaps to the pixel electrode 122 and the data line 60electrically connects to the other pixel electrode 222 and aboutperpendicular to the first and second scanning line 140, 142. Hence,aperture of LCD device is increased. Compared to the prior art, onlymask patterns are changed in lithographic process, to make all TFDs inconformation of scanning lines, such that process cost will not beincreased.

The main advantage of high aperture can be reached to design the fourback-to-back TFDs within the scanning lines. This method includes usingtransparent conductive layer as pixel electrode and first metal layer ofthe TFDs, manufacturing a semiconductor insulation layer, and a metallayer deposited thereon as scanning lines and second metal layer of theTFDs, in which the TFDs are designed within conformation of the scanninglines. Hence, simple process and high yield in this invention can bemaintained.

Although specific embodiments have been illustrated and described, itwill be obvious to those skilled in the art that various modificationsmay be made without departing from what is intended to be limited solelyby the appended claims.

1. A liquid crystal display, comprising: a first substrate; a first pixel electrode disposed on the first substrate; a first scanning line disposed on the first substrate and having a first indentation at an edge of the first scanning line, and the first indentation facing a side of the first pixel electrode; a first metal-insulation-metal diode disposed on the first substrate and within the first indentation, and the first metal-insulation-metal diode electrically connected to the first scanning line; and a second metal-insulation-metal diode disposed on the first substrate and within the first indentation, and the second metal-insulation-metal diode electrically connected to the first pixel electrode.
 2. The liquid crystal display according to claim 1, further comprising a semiconductor insulation layer covering the first pixel electrode.
 3. The liquid crystal display according to claim 2, wherein a material of the semiconductor insulation layer is silicon oxide, silicon oxynitride, tantalum oxide, or carbon nitride alloy.
 4. The liquid crystal display according to claim 2, further comprising a first top layer on the first substrate and within the first indentation of the first scanning line and physically isolated from the first scanning line.
 5. The liquid crystal display according to claim 4 further comprising a first bottom layer disposed on the first substrate and electrically connected to the first scanning line.
 6. The liquid crystal display according to claim 5 wherein the first bottom layer physically isolated from the first pixel electrode.
 7. The liquid crystal display according to claim 6 wherein the first metal-insulation-metal diode is stacked by the first bottom layer, the semiconductor insulation layer and the first top layer, sequentially.
 8. The liquid crystal display according to claim 4 further comprising a second bottom layer disposed on the first substrate.
 9. The liquid crystal display according to claim 8 wherein the second bottom layer extends from the first pixel electrode to the first indentation.
 10. The liquid crystal display according to claim 9 wherein the second metal-insulation-metal diode is stacked by the second bottom layer, the semiconductor insulation layer and the first top layer.
 11. The liquid crystal display according to claim 1 further comprising a second scanning line disposed on the first substrate, paralleled with the first scanning line, and having a second indentation at an edge of the second scanning line, and the second indentation faces another side of the first pixel electrode.
 12. The liquid crystal display according to claim 11, wherein the first indentation and the second indentation respectively extend by an opposite way from the first pixel electrode.
 13. The liquid crystal display according to claim 11 further comprising: a third metal-insulation-metal diode disposed on the first substrate and within the second indentation, and the third metal-insulation-metal diode electrically connected to the second scanning line; and a fourth metal-insulation-metal diode disposed on the first substrate and within the second indentation, and the fourth metal-insulation-metal diode electrically connected to the first pixel electrode.
 14. The liquid crystal display according to claim 1 further comprising a second substrate and a plurality of liquid crystal molecule between the first substrate and the second substrate, wherein the second substrate comprises: a second pixel electrode disposed on the second substrate, and overlapping to the first pixel electrode when the first substrate and the second substrate are sealed; and a data line electrically connecting to the second pixel electrode and perpendicular to the first and second scanning line.
 15. The liquid crystal display according to claim 14, wherein the first substrate is an active substrate and the second substrate is a passive substrate. 